Added rp2_flash ioctl to get the flash fs base address

ports/rp2/rp2_flash.c

@@ -177,6 +177,8 @@ STATIC mp_obj_t rp2_flash_ioctl(mp_obj_t self_in, mp_obj_t cmd_in, mp_obj_t arg_
             // TODO check return value
             return MP_OBJ_NEW_SMALL_INT(0);
         }
+        case 0x1000:
+            return MP_OBJ_NEW_SMALL_INT(self->flash_base);
         default:
             return mp_const_none;
     }